Ⅲ. Results and Discussion
3.4. Source identification
3.4.1 Correlation analysis
24
3.4. Source identification
25 Table 5. Result of correlation analysis between NPAHs and CAPs.
Table 6. Result of correlation analysis between OPAHs and CAPs.
26
Figure 17. Ratio of 9-Fluorenone/Fluorene at each sampling site
Figure 18. Ratio of 7,12-Benz[a]anthracenedione /Benzo[a]anthracene at each sampling site.
Figure 19. Ratio of 9,10-Anthracenedione/Anthracene at each sampling site
27
3.4.2 Diagnostic ratio
Diagnostic ratios represent the ratio of individual compounds with known emission sources, potential emission sources can be characterized as a range of ratios. The diagnostic ratio was calculated to find the potential emission sources of PAHs by land use and season. The ratios of Flt/(Flt+Pyr) and IcdP/(IcdP+BghiP) were used to identify the origin of combustion. For IcdP/(IcdP + BghiP), a ratio below 0.2 means probably contributed from unburned petroleum, between 0.2 and 0.5 implies liquid fossil fuel, and the ratio above 0.5 suggested a grass/wood/coal combustion origin(Yunker et al., 2002). For Flt/(Flt+Pyr), a ratio below 0.5 means petrogenic sources while a ratio above 0.5 suggested a grass/ wood/coal combustion origin(Yunker et al., 2002). The ratio of Flu/(Flu+Pyr) is also used to identify the emission source whether petrogenic or pyrogenic. It is implied to the emission source is petroleum when the ratio is below 0.5. On the other hand, a ratio above 0.5 means that the emission source is coal and biomass burning(Guo et al., 2010; Qiao et al., 2006). In Figure 20, Flt/(Flt+Pyr) and Flu/(Flu+Pyr) were expressed on the scatter plot to understand the characteristics of seasonal emission sources. The scatter plot implied PAHs in spring and summer originated from petroleum sources. In fall and winter, PAHs might be emitted from not only petrogenic combustion but also biomass and coal combustion. Figure 21 was drawn with Flu/(Flu+Pyr), and IcdP/(IcdP + BghiP) by land-use and season. There was no difference in emission sources by each land use. Ulsan seems to be influenced by different emission sources as seasonal. It seems to be influenced by unburned petroleum and liquid fossil fuel combustion in spring and summer, and mainly by liquid fossil fuel combustion and glass/wood/coal combustion in autumn and winter.
Figure 20. Scatter plot of two diagnostic ratios of Flt/Flt+Pyr and Flu/Flu+Pyr.
28
Figure 21. Two-scatter plots of two diagnostic ratios of Flu/Flu+Pyr and IcdP/IcdP+BghiP by season and land-use.
In the case of NPAHs, the diagnostic ratio was identified to determine the effects of primary emission and secondary formation. The ratio of 1-NNap/2-NNap is used to identify whether it is reacted by OH radicals or nitrate(Sasaki et al., 1997). A ratio above 2 suggests the formation reaction occurs by the dominance of the nitrate. Meanwhile, A ratio less than 2 means the formation reaction occurs by the dominance of the OH radicals. In Figure 22, most of the sites have lower than 2 suggesting that nitronaphthalene might be formed by secondary formation by reaction with OH radicals. However, it shows a value of more than 2 in the fall and winter at the U10 site. Compared to the spatial distribution of NO2 and the ratio of 1-NNap/2-NNap, the highest concentration of NO2 was observed at U10. It suggests that nitronaphthalene may have reacted with nitrate to form a secondary product.
The following diagnostic ratio was 2+3-NFlt/2-NPyr which is used to identify secondary formation pathways(Chuesaard et al., 2014; Zielinska et al., 1989). A ratio close to 100 suggests the dominant reaction with nitrate during nighttime meanwhile, a ratio less than 10 means the dominant reaction with OH radicals during daytime(Y. Zhang et al., 2018). In figure 23, the ratios of 2+3-NFlt/2-NPyr were less than 10 at most of the samples. It suggests NPAHs might have formed via OH radical- initiated reaction in the daytime. The following diagnostic ratio was 2+3-NFlt/1-NPyr which is known that the effect of the secondary formation when the ratio is higher than 5, the effect of primary emission is clear when the ratio is lower than 5(J. Zhang et al., 2018b). In Figure 24, it shows the ratios were higher than 5 at most of samples. Except for a few samples at urban sites in the spring, it implies that NPAHs are primarily formed by secondary formation.
29 Figure 22. Diagnostic ratio of 1-NNap/2-NNap.
Figure 23. Diagnostic ratio of 2+3-NFlt/2-NPyr.
Figure 24. Diagnostic ratio of 2+3-NFlt/1-NPyr.
30
3.5 Risk assessment
BaPeq was calculated with individual concentrations and toxic equivalent factor (TEFi). The averages of fraction and TEQ were expressed by seasonal (Figure 25). The average of TEQ shows highest in winter (0.378 ng-TEQ/m3), followed by spring (0.376 ng-TEQ/m3), fall (0.337 ng-TEQ/m3), and summer (0.229 ng-TEQ/m3). There was no difference between each season except for summer. In terms of fraction, PAHs not listed in EPA had high portion, followed by 13 PAHs listed by US-EPA and ∑NPAHs. NPAHs contributed relatively low to the TEQ about 1-2% due to the low concentration.
However, it should not be overlooked because NPAHs did not have many toxicological studies yet compared to PAHs, so most NPAHs do not have TEF values. Even OPAHs also do not have available toxicity coefficient values.
Figure 25. (a) Fraction and (b) Toxic equivalent concentration (TEQ) by seasonal.
Figure 26. Stack bar of the total incremental lifetime cancer risk (ILCR) of PAHs and NPAHs.
31
The potential cancer risk was assessed using the model of incremental lifetime cancer risk (ILCR).
The seasonal averages of ILCR were drawn in Figure 26 and listed as winter (6.799E-08), spring (6.513E-08), fall (5.710E-08), and summer (2.215E-08) in the order of seasonal high risk. The average risk at all seasons in Ulsan was lower than the US EPA (1.0E-06 or 1.0E-04) and WHO (1.0E- 05) risk criteria. Therefore, it seems to be a safe level.
In order to understand the spatial distribution of cancer risk, the ILCR values of PAHs and NPAHs calculated for each site were interpolated using inverse distance weights (IDW) in ArcGIS (Figure 27- 28). For PAHs, the cancer risks were high in nonferrous metal industrial areas and petrochemical industrial areas in spring and summer. Compared to the spatial distribution of PAHs concentration, the pattern was quite similar. However, PAHs concentrations were low at the U3 site, but the risk was high in the spring. Non-ferrous metal complexes (I5) and petrochemical complexes (I2 and I3) have a high risk the damage to local residents is small due to their low population density. However, the area having higher levels of risk moved to near the automobile industrial area (U2) in fall and winter. In terms of NPAHs, the spatial distribution of cancer risk was slightly different from PAHs. The impact of the automobile industrial complex was hardly seen, and the impact of the non-ferrous metal industrial complex (I5) was clearly confirmed. It suggests that NPAHs having TEFi were related to industrial activity from the non-ferrous metal industrial area.
32
Figure 27. Spatial distribution of the total incremental lifetime cancer risk (ILCR) for PAHs.
Figure 28. Spatial distribution of the total incremental lifetime cancer risk (ILCR) for NPAHs.
33
Ⅳ. Conclusion
This is the first study that investigated PAHs, NPAHs, and OPAHs together using passive air samplers in Korea. In this study, the levels of each target compound were investigated by 20 sites. The average concentration of PAHs, OPAHs, and NPAHs was similar with previous studies. Low molecular weight (LMW) and middle molecular weight (MMW) compounds having 2-, 3-, and 4- aromatic benzene rings were mainly detected, meanwhile high molecular weight (HMW) compounds having 4-, 5-, and 6-rings (7,12-DMBaA, 3-MCA, 1,6-DNP, 1,3-DNP, and 1,6-DNP) were not detected. In terms of seasonal variation, the concentration of PAHs is highest in fall by following winter, spring, and summer. On the other hand, NOPAHs were not influenced by significant seasonal changes due to the secondary formation during the summer. In terms of spatial distribution, PAHs were greatly influenced by the non-ferrous metal industrial complexes and petrochemical industrial complexes when the east wind blew during the warm seasons, but the impact of the automobile industrial complex was clearly identified as evidence of potential emission sources during the cold season that blew northwest wind. In particular, OPAHs were greatly influenced by automobile industrial complexes while the impact of nonferrous metal complexes decreased. However, there is no specific potential emissions sources of NPAHs. Because they were simultaneously affected by primary emission and secondary formation.
The relationship between target compounds and CAPs was identified through correlation analysis.
There was a high correlation between parent PAHs and derivates PAHs, which were expected to have similar potential emission sources. However, NO2 and some NOPAHs show a negative correlation, suggesting the possibility of secondary formation. The emission sources and formation pathways of PAHs and NPAHs were investigated using the diagnostic ratio. As a result of diagnostic ratio, NPAHs were mainly formed via secondary formation with OH radicals during the daytime. In the case of PAHs, it was confirmed that they were mainly affected by liquid fossil fuel combustion, greatly influenced by petroleum evaporation in warm seasons, and greatly influenced by biomass burning and coal combustion in cold seasons.
The potential cancer risk was evaluated by the model of ILCR and was not higher than the criteria of UEA-EPA in all samples. Not listed PAHs contributed to the high portion of cancer risk, meanwhile NPAHs contributed to just 1%. However, derivate PAHs should not be overlooked because the available toxicity coefficients are limited. The spatial distribution of PAHs and NPAHs was confirmed using the ILCR value calculated at each sampling site, respectively. It showed some different tendencies compared to the spatial pattern of concentration. In the case of PAHs, high risk was identified in the U4 area, where the concentration was low. It needs to control PAHs because this site
34
is high population density than an industrial area. For NPAHs, high risk was identified especially in non-ferrous metal industrial complexes suggesting that NPAHs having toxic coefficients were emitted in non-ferrous metal industrial complexes.
In this study, the seasonal and spatial variation were confirmed to identify the level of target compounds (PAHs, OPAHs, and NPAHs) and their potential emission sources using PAS-PUF in Ulsan, which is large industrial area. These results can be used as basic data for domestic NOPAHs research in the future. However, long-term monitoring is required to clearly identify the emission source of contamination. Since PAS-PUF mainly collects gas phases, there are limitations in using diagnostic ratio and identification of long-range transport. To solve these limitations, it is necessary to predict the particulate concentration with gas-particle partitioning and correct the concentration.
Further studies on particulate NOPAH using an active air sampler are also necessary to clearly identify gas-particle distribution on NOPAHs in Korea.
35
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